The immune systems of humans and animals are amazingly complex and have mechanisms for protecting the host from ill effects caused by foreign chemical or biological substances which enter the host in some manner. Such foreign substances include haptens, antigens, viruses, microorganisms, drugs, hormones, plant lectins and other substances readily apparent to one skilled in the art. In this application, such substances are identified as "ligands". When a host is invaded by a ligand, the host normally produces proteins in response which will complex specifically with the ligand. Such proteins are known as antibodies. It is often desirable to detect the presence of ligands for appropriate diagnosis and treatment.
However, sometimes, the ligand cannot be readily detected, for example where it is masked by other materials in the host or is present in very low concentrations undetectable by standard assays. Because antibodies react specifically with a corresponding ligand to form immunological complexes, the presence of antibodies is often detectable when the presence of the ligand is not. Using immunological reactions, then, it is sometimes possible to design assays to detect the antibodies as an indication of the presence of the ligand.
In other instances, antibodies are present in a host organism because of autoimmune responses, that is, in an abnormal situation when antibodies are produced against the host's normal tissues, cells or organs. Detection of the antibodies in such instances may help identify pathological activities in the host.
Viruses present in humans and animals are a major healt concern today, not only because of the effect they have upon the host organism, but also because of a continuing need for improved means for detection, diagnosis, treatment and contamination prevention. Some viruses do not harm the host organism while others merely cause minor discomfort or temporary inconveniences. Still others, however, may cause serious illness and result in death.
There are, then, obvious reasons to detect the presence of viruses in host organisms quickly for effective treatment, appropriate health safety measures or for screening biological fluids, tissues or organs which may be used by another human or animal.
Virus particles and virally infected cells contain specific antigenic components which can induce an immunological response to produce antibodies specific to the components. In some instances, the antigenic components can be detected in vitro using antibodies specific thereto. However, in other instances, it is easier or more expedient to detect the antibodies produced in the organism.
Human retroviruses, as a family, represent a group of related exogeneous retroviruses which exert a significant proliferative or cytopathic effect upon the target T-lymphocytes they infect. The resulting effects of these retroviruses include T-cell proliferation leukemia, T-cell depletion and immunosuppression in humans infected by the viruses. These retroviruses are known as the HTLV (human T-cell leukemia-lymphoma virus) and HIV (human immunodeficiency virus) families of T4 tropic retroviruses.
The first human retrovirus discovered, (HTLV-I), appears to represent the etiological agent of mature T-cell leukemia and lymphomas as typified by adult T-cell leukemia (see, for example, Poiesz et al, Proc. Nat. Acad. Sci., U.S.A., 77, 1980 and Yoshida et al, supra, 79, 1982). At present, the presence of HTLV-I and T-cell malignancies are believed to occur at increased rates in the populations of certain Caribbean islands and southern Japan, but HTLV-I is now widely recognized as a worldwide medical concern. People infected with HTLV-I or having come into contact with the virus generally have antibodies directed against HTLV-I in their body fluids, and especially in their blood. In addition, a significant portion of the patients suffering from the neurological disorder known as Tropical Spastic Paraparesis possess antibodies to HTLV-I.
Continuing research has determine that there are several additional retroviruses which are of significant medical importance. Besides HTLV-II, a third virus was discovered and identified variously as HTLV-III, Lymphadenopathy Associated Virus (LAV) and HIV-I (described below).
Acquired immune deficiency syndrome (AIDS) is a relatively recently recognized disease evident in several parts of the world. It has been observed that the disease is predominant in certain high-risk segments of the population of certain countries, including practicing homosexual men, illegal intravenous drug users, hemophiliacs, blood transfusion recipients and those having intimate heterosexual relationships with these high risk groups. It has been discovered by U.S. and French researchers that the disease is spread by the transmission of the retrovirus HIV-I.
No cure has been found to date for AIDS, and medical and scientific observations indicate that it is unlikely a cure will be found within the near future. Moreover, it is well known that all sufferers from the disease are likely to die. These tragic consequences have spurred the urgency in medical and diagnostic research associated with this disease.
As with other viral diseases, exposure to or infection from HIV-I produces an immunological response, that is the production of antibodies. More specifically, antibodies to antigens of the virus have been detected by researchers and clinicians in many sero-epidemiologic studies. A number of human biological fluids are considered vectors for HIV-I infection. Human blood is the primary biological fluid in which the virus or antibodies therefor are found. While people having HIV-I antibodies in their blood may not necessarily also carry the virus or themselves develop AIDS, there remains a serious concern about viral transmission through contact with or donation of blood by such individuals. Hence, there is continuing research and development to provide rapid and sensitive assays for detecting the presence of HIV-I antibodies in blood samples. Blood banks have an obvious interest in screening donated blood to insure a virus-free supply. Medical and dental practitioners in hospitals and offices need diagnostics tests to adequately protect other patients as well as themselves from viral infection.
Many immunological techniques are known for detection of antigens or antibodies, including HIV-I antibodies. For example, U.S. Pat. Nos. 4,520,113 (issued May 28, 1985 to Gallo et al) and 4,708,818 (issued Nov. 24, 1987 to Montagnier et al) describe radioimmunoassays, Western blot techniques and ELISA (enzyme-linked immunosorbent assay) for HIV-I antibody detection. A competitive ELISA is described in E.P. Publication 234,941 (published Sept. 2, 1987).
While a number of useful assays are known, they generally require hours to perform (see for example, E.P. Publication 234,941, Example 5) and may also require extensive equipment and complicated protocols in order to obtain accurate results. This adds to the expense of the test as well as the likelihood of error.
Moreover, such tedious and time-consuming tests are not suitable for instances where a determination of the presence of a retrovirus (or any other virus) is needed quickly. For example, practitioners or clinicians in police stations, trauma centers, hospital emergency rooms, immigration offices and dental and medical offices may need to know if patients are infected with a given virus immediately. A rapid viral test would be a significant advance for such instances. Also, rapid viral tests would be highly valuable for use in remote parts of the world where conventional medical or testing facilities are nonexistant.
Hence, there is a need in the art for a rapid and sensitive assay for viral antibody detection in biological specimens.